# Man Page set_intersection.3

```
Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

```

## NAME

```     set_intersection

- A basic set operation for constructing a sorted intersec-
tion.

```

## SYNOPSIS

```     #include <algorithm>
template <class InputIterator1, class InputIterator2,
class OutputIterator>
OutputIterator
set_intersection (InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2,
InputIterator last2,
OutputIterator result);
template <class InputIterator1, class InputIterator2,
class OutputIterator, class Compare>
OutputIterator
set_intersection (InputIterator1 first1,
InputIterator1 last1,
InputIterator2 first2,
InputIterator2 last2,
OutputIterator result, Compare comp);

```

## DESCRIPTION

```     The set_intersection algorithm constructs a sorted intersec-
tion  of elements from the two ranges. It returns the end of
the constructed range. When it finds an element  present  in
both ranges, set_intersection always copies the element from
the first range into result. This means that the  result  of
set_intersection is guaranteed to be stable.   The result of
set_intersection is undefined if the result  range  overlaps
with either of the original ranges.

set_intersection assumes that the ranges  are  sorted  using
the  default  comparison  operator  less than (<), unless an
alternative comparison operator (comp) is provided.

```

## COMPLEXITY

```     At most ((last1 - first1) + (last2 - first2)) *  2  -1  com-
parisons are performed.

```

## EXAMPLE

```     //
// set_intr.cpp
//
#include <algorithm>
#include <set>
#include <iostream>
using namespace std;
int main()
{

//Initialize some sets
int a1[10] = {1,3,5,7,9,11};
int a3[4]  = {3,5,7,8};
set<int, less<int> > odd(a1+0, a1+6),
result, small(a3+0,a3+4);
//Create an insert_iterator for result
insert_iterator<set<int, less<int> > >
res_ins(result, result.begin());
//Demonstrate set_intersection
cout << "The result of:" << endl << "{";
copy(small.begin(),small.end(),
ostream_iterator<int,char>(cout," "));
cout << "} intersection {";
copy(odd.begin(),odd.end(),
ostream_iterator<int,char>(cout," "));
cout << "} =" << endl << "{";
set_intersection(small.begin(), small.end(),
odd.begin(), odd.end(), res_ins);
copy(result.begin(),result.end(),
ostream_iterator<int,char>(cout," "));
cout << "}" << endl << endl;
return 0;
}

Program Output

The result of:
{3 5 7 8 } intersection {1 3 5 7 9 11 } =
{3 5 7 }

```

## WARNINGS

```     If your compiler does not support default  template  parame-
ters,  then  you  always need to supply the Compare template
argument and the Allocator template argument. For  instance,
you need to write:

set<int, less<int> allocator<int> >

set<int>

If your compiler does not support namespaces,  then  you  do
not need the using declaration for std.

```

```     includes,       set,       set_union,        set_difference,
set_symmetric_difference

```